1. Field of the Invention
The present invention relates to a call admission control method for properly allocating a network resource and a flow-monitoring method for monitoring traffic of terminals during communication in a network accommodating terminals having various traffic characteristics.
2. Description of the Related Art
In an asynchronous transfer mode network (generally called an "ATM-network") in which all communication information are subjected to transmission/switching by a fixed length block called a "cell" including a header having a virtual-channel id (VCI), information belonging to different virtual-channels on a line are statistically multiplexed by asynchronous cell multiplexing. Therefore, in accordance with amounts of information generated from terminals having various traffic characteristics, the network can dynamically allocate a transmission bandwidth and realize efficient transmission/switching.
In addition, a switching operation for each communication information can be performed at high speed by hardware since a virtual-channel id (VCI) is referred to for each cell. Therefore, this asynchronous transfer mode network has flexibility in bandwidth utilization of a conventional packet switching network and a real-time property of a conventional circuit switching network. As a result, communication including various types of media; for example, voice, still image, motion image, and high speed data is realized.
Transmission rates, however, of the communication information described above are different in respective terminals, and a generation form of the information tends to have burstiness. Therefore, a utilization state of network resources such as transmission-lines and switches varies dynamically. As a result, the network cannot perfectly grasp the utilization state of resources.
If the resource utilization state is not perfectly grasped, the network may excessively allocate a resource to a terminal or reject a call-setup request from a terminal even if an additional resource is present.
In the asynchronous transfer mode network, no flow-control is performed in a network unlike in conventional packet switching. Therefore, if a resource is excessively allocated to a terminal, the number of stored cells in a sending/receiving buffer of a switch is increased. As a result, transmission delay time is increased or a cell loss occurs to degrade communication quality. In the worst case, the network itself causes a congestion-state.
To the contrary, if a network keeps an unnecessarily large amount of resources and rejects an admissible call-setup request, the resources cannot be efficiently used to degrade admission quality of the call.
As described above, in the asynchronous transfer mode network, terminals have a wide range of transmission rates from low to high rates, and the traffic characteristics often have burstiness. Therefore, it is difficult to correctly grasp a change in network resource utilization state. For this and other reasons, proper network resource allocation capable of accepting call-set-up requests as many as possible within an allowable range as communication quality cannot be performed.
Therefore, the network, e.g., a switch must correctly grasp characteristics of the cell-flow of an individual call and sequentially, numerically express a predicted traffic-load of a line as one characteristic of cell-flow, thereby achieving maximum communication power of a network resource.